


Fragments

by Noire73



Series: The Underground [1]
Category: Undertale (Video Game)
Genre: Backstory, Basically full of headcanons, Dad!Gaster, Gen, My First Fanfic, a bit of self hate (i guess), don't really know how to write arguments
Language: English
Status: Completed
Published: 2016-03-29
Updated: 2016-03-29
Packaged: 2018-05-29 20:09:48
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 4,798
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/6391561
Author URL: https://archiveofourown.org/users/Noire73/pseuds/Noire73
Summary: <blockquote class="userstuff">
              <p>Sans get's curious of his father, the Royal Scientist, most secret projects and decides to dig around his archives.</p>
            </blockquote>





	Fragments

**Author's Note:**

> Okay, first fanfic. Yeah! 
> 
> Just before we start, I'm clearing just a few headcanons:
> 
> * Gaster is both Papyrus and sans father.  
> * Sans is doing his internship in Gaster's lab.  
> * Gaster was one of the few monsters who lived the war and is still around.  
> * Gaster and Asgore have known each other since before the war and are close friends.  
> * Gaster can speak but has a weird accent so he signs as he speaks. His dialogs are in bold.
> 
> Bold text is Gaster speaking,

Gaster kept a lot of mystery on his past projects including the most resent one, the Gaster Blasters, which he had made 2 for each one of his sons as well as for himself and had somehow kept it a secret from everyone. Sans decide to look for any clues in the reports in his father's many archives while he was away on the monthly meeting with the heads of each department.

 

He didn't like being kept in the dark, especially not on something so advanced as the Blasters.

 

Is true that sans had just started his internship on his father's science division and was left out of some mayor projects but in the end, the Royal Scientist was _his_ Father, there was no need for him to keep them in secret, it had only made him even more curious, and gosh darn he had to inherit his stubbornness. Then again, his father had issued him that if he was to work in his department, sans was to refrain from calling him “father” or “dad” so that a sense of professionalism would remain. Colleges at works and nothing else.

 

But sans being sans, it took him less than a week to befriend his boss. Gaster was surprised on how natural his interactions where with him during work hours. They would chat on little things, discuss theories, they even had a few verbal confrontations regarding them and conflicting points of view. Sans even got used to calling him Doctor or simply by his name, which was weird for Gaster at first. It felt just like he was another friend and college; no sign of any fraternal sentiment or family issues. It was kind of nice. And the best part was that once they were home they would continue on their little pet projects. They once managed to make a self-sustained tornado.

 

They trusted each other as a family and as colleges. 

 

Even still, with all that trust, Gaster kept secrets from him. Secret projects and information that has been weighting down on his soul. Sans decided that if his father wouldn’t tell him, then sans would have to find out on his own. He used this opportunity to research Gaster’s archives to see if he could find any leads. 

 

Most of his reports where of his findings, his theories and plans for projects that were developed by his scientist. Apparently he kept the ones he felt most proud of, like the report for the activation of the Core, the communication towers around the Underground, the elevators, the Gaster Blasters, the tea maker, the conveyor be- sans back track a few folders.

 

_The Gaster Blasters._

 

He took out the folder and flip it open. In it there were reports as well as journal entries describing the process and statistics of the Blasters. In the journal pages there where a few notes in Windings of observations and pieces of trivia his father had wrote unfortunately some were fast scribbles that he barely understood sometimes. His calligraphy could be messy when he wrote fast.

 

One of them read: _**"Cannot afford using fragments like on the first ones to give them some extent of sentience. The consequences would be lethal."**_ Fragments? The first ones he made? Had his father been working on this for longer than he had said?

 

He kept reading but the rest didn’t had more pertinent information. There was a code he repeated in a few notes: WP01. He supposed those where the code name for the first prototype.

 

The report was settled back in the archives. He now knew what he was looking for.

 

He read the names on the tags searching for any lead on the prototypes. There was no need but it had peeked his curiosity even more.

 

At the back of the drawer was a small folder pertaining to WP01. Jackpot. He flipped it open and started speed reading it.

 

 _ **"Removed a small fragment to use on the experiment. Time will heal it. It has happen before."**_ Fragment? Heal? Did his father used a soul for WP01? He had heard rumors around the lab of Gaster experimenting on himself number of times in the past.

 

 _ **"Wonder what would happen if I used a very small dose of DT? Have to observe any changes"**_ DT? He used Determination in his experiments??

 

 _ **"If this doesn’t work I’m not risking another try. It’s healing slower than expected. If I used another one it could be lethal."**_ He WAS using his soul. Sans didn’t want to believe the rumors because, well, it was his father they were talking about.

 

_**"It's starting to take form. It resonates a high level of magic. In a few weeks I will be able to enhance it more."** _

_**"There is something wrong. I don’t know if I should continue. But I don’t want that piece of soul go to waste."** _

_**"Magic levels appear higher. This might be a groundbreaking scientific discovery. We could use WP01 to break the barrier. If things get south with the humans again, it might work against then as well."**_ A weapon. Like the Gaster Blasters.

 

_**"There.... has been an unpredictable result. Miscalculations where made. If I don’t find a way to fix it, the consequences will be grave."**  _

_**"The danger was averted. Asgore is mad at me. Why wouldn’t he? I put myself and the people on the lab in danger. But I can’t seem to care. The result were unpredictable but none the less very accepted. His magic is extremely high but his stats are not optimal. I'll have to keep an eye on him.** ”_

 

The next entry was very short, the letters were almost unreadable scribbles he had to read it over and over again. His soul skipped a bit.

 

_**“I can’t believe I did it. He is such a precious thing. This is the best thing I have ever done in my life"** _

 

Sans dropped the file, watching absent mindedly at the scattered paper. His mind still processing everything. 

  
  
His father was creating a weapon to destroy the barrier. Using his own soul and DT.

 

He created a sentient weapon, sans.

 

Sans was a weapon. And according to the file, Papyrus was as well.

 

He suddenly found it hard to breath. His eyesight was getting blurry, he felt tears running down his cheekbones. Sans rubbed his face aggressively with his sleeves. 

 

Sans felt angry and betrayed. He wanted to find his fath- ... Gaster. He wanted to find him and punch him so hard across his cracked skull. He felt disappointed. All this years, Gaster had been raising tools to break the barrier and to protect Monsterkind if things went wrong again.

 

He clenched his fists, if he had skin his knuckles would probably be white right now. He could feel his magic boiling "calm yourself. Breath you bone head." He tried calming himself.

 

No one must see him like this. Sans needed to confront daddy dearest about this

  
15 minutes until their break.

 

\---------

 

Gaster had been dreading the meeting since the last one a month ago.

 

The meetings where so the head of the each departments could get together for brainstorming and report advances on their projects. Gaster didn’t particularly wanted to be in this one. Since the 5th human fell down there where quite a lot of advances in each department, especially in the magic and medical ones. But still, no headway in how to break the barrier. He had really wanted sans to be there with him but he didn’t want to show favoritism towards him; a few more months and sans could apply to be his assistant once his internship ended.

 

As he walked back to his office, he felt a strange sensation on 'the pit of his stomach'. Why would he though? Everything was in order. Papyrus was in class, sans said he wanted to run some tests on his own. He was sure he didn’t leave anything dangerous on so… why did he felt like this? He shrugged, if it was important it will get back to him.

 

Gaster opened the door to his office and entered. As he turned around to face his desk he received a folder straight to the face; he grabbed it with his magic before it fell. He was ready to face against anyone, anyone except sans.

 

**"What are you doing here, son? Did you not say-"**

 

"shut up." He growled through his teeth. "don’t call me that." His voice was low and serious.

 

 **"sans... what's wrong?"** Gaster tried to reason. He looked down for a moment to see the file, it was familiar. He read the tag. A breath got stuck in his throat. **"Where did you..."**

 

" _Magic levels are high. We could use it to break the barrier OR against the humans._ " sans voice grew louder trying to imitate Gaster accent.

 

 **"Why do you have this?"** Gaster sounded serious, almost wounded.

 

"that doesn’t matter. why did you never told me?" He felt his anger growing.

 

 **"Yes, yes it matter. You shouldn't be looking through my stuff."** He scolded.

 

"well I wouldn’t have to if you had actually trusted me!" He was yelling now. 

 

**"This... this is no place to discuss this, we should-"**

 

"yes it does. i'm an experiment. where else to talk about it then at the lab of its creator." He was spitting poison with each word he said.

 

 **"sans! Dont talk like that. Let's go somewhere private"** He reached out barely grabbing sans sleeve. Gaster teleported them to their apartment’s living room. Papyrus was at school and the neighbors were at work; this was as private as they could get.

 

"Let go of me!" Sans yanked his arm away from Gaster.

 

 **"Okay, now I need you to calm down and let me explain."** Gaster felt himself lose his patience slowly.

 

"explain what? that you created me... you created us, to be weapons?? just tools to use once we are ready?" He had nothing to hold back now that they were alone. "that all our lives are complete lies!?"

 

 **"No that's..."** he felt how his patience was abandoning him. “ **Technically speaking, every parent CREATE their children."**

 

"You know exactly what I mean!"

 

**"The fact that you were not conceived the traditional or natural way doesn’t devalues the fact that you are my sons."**

 

"i wasn’t even supposed to be your son! i was supposed to be a tool! a mere accident!"

 

 **"Aww come on sans."** He was tired of hearing his son refer to himself as an object. His patience was dwindling. **"You are not a tool and an accident is not a bad thing. I've known a lot of monsters who were accidents, it’s nothing special!"** He immediately regretted saying that as he saw the wide eyes of sans staring back at him, wounded. His frustration had gotten the better of him and he was paying the price.

 

"Nothing special, huh?"

 

**"No sans I didn’t-"**

 

"stop. i don’t want to hear it." He took a few steps back. "you know what? i don’t want to hear anything else from you." Sans stomped out of the apartment, slamming the door just for the heck of it. Gaster had little time to react. He swung open the door and stepped outside, of course he wouldn’t be there anymore. He closed the door, leaning his back to it. He had to find sans and apologize. He had to find him before he did something crazy.

 

\---------

"what a sanstastic day to be alive..." sans sighted. He couldn’t believe Gaster had said that. He knew he could be direct and talk before thinking but, he expected something different from him. He did wanted to hear his explanation. His whole life had crumbled in seconds; he had a vague idea of his own identity before and know... he didn’t even know who he was. What he was.

 

In his anger, he had teleported to the back of his favorite restaurant, Grillby's; the last few years he had been frequenting the restaurant even more than his father... the ambience and the locals where warm for such a harsh cold; the perfect place to relax. The main reason that he came here where for the food and the cook that prepared it. Grillby was a very good listener and would generally find himself telling him a lot of his worries. Sans really wanted to talk to him right know but... Gaster would find him immediately and he didn’t want that. He backed away from the restaurant, he would get to talk with Grillby some other time.

 

He teleported again to a place he was sure Gaster wouldn't find him. In an instant, sans was in a little cave in Waterfall. The only place it could be accessed by the river and he was sure Gaster didn’t know about this place. The only other thing in the cave was a bench where sans had taken countless naps.

 

He sat down on it, throwing his head back to rest it in the bench. With a sharp groan, he lean forward, propping himself on his elbows, covering his face with his hands. He was exhausted, teleporting from Hotlands to Snowdin was taxing enough, and he had to crown it with another one to Waterfall. His self-restrain was fading. He felt himself crumbling down, he was on the verge of tears.  
He felt something shifting in his vicinity but he had zero cares right now.

 

 **"sans..."** said a familiar voice.

 

Sans lift his head in a snap. Gaster was looking at him, he looked embarrassed. 

 

"how did you-" sans stood up.

 

 **"I know the Underground like the palm of my hand…"** he looked down his at his hands, **“Although… well… heh, there’s not much of my palm to know about…”** he tried joking; sighting as he saw sans’ annoyed expression. **“sans, please listen to me."**

 

"I said I didn't want to hear anything from you" he teleported again. He was once again in Snowdin, just a few steps from the Inn. 

 

 **"You have to let me explain"** Gaster said from behind him giving sans a -what could be described-mini heart attack. **"Stop jumping around everywhere."**

 

"Shut up!!" He was now near the entrance to Hotlands. Sans was feeling out of breath.

 

**"You are going to over exert yourself. You need to stop."**

 

"How you keep doing that?!" He started patting around his clothes. "Do you have some sort of tracker in me or something?"

 

**"I would never do such a thing, you know that."**

 

"no, i dont know you anymore." He tried to yell but he was starting to feel exhausted; Gaster had taken the same jumps and he didn’t even seemed bothered.

 

 **"Sans, please let me explain."** He took a step forward, preparing himself to catch sans if he were to teleport. 

 

"I  d o n ' t  w a n t  t o  l i s t e n  t o  y o u r  e x c u s e s." sans knew very well that he was being unreasonable. He jumped again. This time falling to his knees on the forest. Sans expected to feel the coldness of the snow but instead was met with fabric. Gaster had teleported with him and was holding him by his arms. "how do you... keep doing that...?" He tried pushing him away but to no avail, he was far too tired.

 

 **"I've had this ability for ages, I know a few tricks."** He held him tightly. **"Maybe I can show you one or two someday..."**

 

Gaster tried to encircle him in a hug but sans push him away with as much strength as he could muster.  
"don’t! don’t touch me..." sans staggered backwards. "just... you know what? im too tired of... of everything... whatever you want to say..." he sighted, covering his face with his hands. "out with it then."

 

 **"A-alright..."** Gaster approached sans, resting a hand in his shoulders. Before he had time to react, they were both back at the little cave with the bench. **"I figured this would be more comfortable."**

 

"Whatever..." sans slumped down on the bench.

 

 **"Okay, but I need to you to promise me you will let me finish and won’t try to get away until I’m done."** He looked distress; sans nodded.

 

"sure... is not like you won’t keep following me around until you do."

 

 **"Thanks..."** sans just shrugged it off. Gaster took a deep breath, this would not be easy at all.

 **"Yes is true that the original plan was to create something powerful enough to destroy the barrier."** He started fidgeting his fingers. **"In the spur of the moment, I decided to use a very small fraction of my soul to see what would happen. That last attempt was going to be my last one, so I got creative; a thought crossed my mind: can we somehow create our own monsters, not necessary to fight but to see if I could. As time passed, it was clear I wasn’t creating a simple 'weapon', and the consequences of carrying on with the experiment would be dangerous, both for me and the subject, WP01.  
"I could have put a stop to it whenever I wanted, but I was so determined to see it through that the consequences weren't important. Up until this day, I am grateful for that moment of stubbornness. Otherwise..."** Gaster looked grim for a moment; sans shifted uncomfortably on the bench as he watch the other pace from one side to the other.

 

"Otherwise...?" Sans inquired.

 

 **"I probably wouldn’t be here at all."** He whispered, making it very difficult for sans to catch it. **"SO, one day, I decide to keep working on WP01, I had planned to augment its magical capabilities in case it actually worked as intended to, but... during the second try... the machine that harbored the small soul overcharged. The explosion devastated the whole room. I was of course injured, but my mind would not let me hurt until I knew what had happened to WP01.**

 

**"As the smoke cleared out, I approached the machine; many thoughts rushed into my mind: what went wrong, what happen to the subject, did I fail. A sound caught me off guard. A cry. The cry of a baby. My mind went blank, the only thing I managed to do was run towards it; I almost fell a few times."**

 

A soft expression crossed his face. **"Then, I saw you. A little pile of baby bones crying on the pedestal's machine."** Gaster stop to look at sans. **"As I held you in my arms the world stopped. I only noticed everything around me until Asgore found me. I was so in trance that when I passed you to him, I hadn’t felt how exhausted I was until I collapsed."** He chuckled under his breath, he grabbed his hands behind his back. **"And… that’s how you were born."** His voice a little quieter.

 

"By... a failed experiment..."

 

 **"N-no... it didn’t failed exactly.”** He gestured wildly with is hands. **“The result was unpredicted but I wouldn’t have done anything differently."** He said proudly. 

 

Sans factions had soften during the explanation. Yes, he got it, Gaster had manage to emulate monster birth without the need of both parents.

 

But there was something bothering sans.

 

"okay, i get it now. just a question and don’t get me wrong on this, but if the consequences are so taxing then why make another one?"

 

Gaster had expected that question. He took another short breath, this was going to be a bit longer to explain.

 

**"For you to understand why, I need to tell you… a story.”**

 

Sans braced himself, he had never heard his father talk this much, not even in their home. It was a bit unnerving trying to listen to him and see his hands moved around. He nodded when he saw Gaster’s worried expression.

 

He took a breath, which really didn’t need but calmed his nerves. **“Before the war, I met someone, extraordinary. She was a general for the Royal Army serving under the former king. She was strong, an excellent tactician, charismatic, a commanding leader. She was respected and loved by his peers and at the time, by me as well.**

 

**“When I met her, I was just a small scientist appointed to work under... his majesty’s Royal Scientist at that time. We were preparing for the possibility of war. We investigated on how to amplify magic and was later working together with the military force. That’s when I saw her. They were training and I found myself not looking away from her as she fought her trainees. She noticed and turned to look at me with a fierce expression.**

 

 **“I had never felt so small.”** He paused for a moment to rub his hands, they were starting to hurt. He knew that with his sons there was no need to sign but at this point it was a habit.

 

 **“After that we would bump each other regularly on tests or trainings. She offered to train me in case of an emergency and of course, I accepted. Through her, I met Gerson, Asgore and Grillby's Father. We married a few years after; and then, a decade or so later, the war started."** Something dark appeared on Gaster's face for a brief moment.

 

 **"Well, its kind obvious what happened seeing as she is no longer here."** He intertwine his fingers holding them tight. **"The day that we were cast down here, everyone was trying their hardest to push them back, but it was useless... she was fighting with all her might against two. She managed to defeat one but... she..."** he closed his eyes, the memory still haunted him. He went quiet for a moment.

 

"gaster?" Sans asked worried. "dad?" 

 

He snapped back taking a few breaths. **"We... made a promise, that once everything was fine and we were safe, we would have a family and live happily ever after... heh...... what a beautiful fantasy don’t you think?**

 

**"She wanted children as much as I. She had a whole future planned and... That day, our future crumbled. I... I was a mess after that. I had lost HOPE on everything, but the new King and Queen wouldn’t let me falter. I went through life with the single purpose of helping Asgore break the barrier. A few projects here and there got me motivated and determined, but I had nothing to gain or lose, I was just moving forward without meaning or direction. Until you were born.**

 

 **“You became a beacon for me, something to look after every day I woke up."** He looked at sans a bit embarrassed.

 

 **"I remembered our dream to form a family whenever I looked at you. I had made a promise to her, and knowing that I could create a monster on my own, it got me determined."** He smiled resting a hand on his chest.  **"Guess how many she wanted to have."**

 

Sans chuckled for a moment. "two..."

 

 **"Exactly!"** He said with a smile that quickly faltered. **"But see, I had to wait a while."** he closed his eyes and concentrated, a light started to brightly illuminate from within this chest. He winced as he pulled out his soul.

 

That was wrong, sans thought, one shouldn't be able to hurt from doing that, but once the soul was in view he understood why.

 

In Gaster's hand, floated a small fractured heart. **"This is... what happens when you use yourself as a test subject."** He frowned. **"The cracks have been healing slowly. I calculate that maybe in a decade or so it will be fully healed."**

 

Sans didn’t know what to say, he just observed. It wasn’t his fault but he couldn’t help feeling guilty.

 

 **"Don’t worry, it was already like this before you were born."** Gaster had seen sans hunching on his seat and tried to comfort him but it came out weird and nonchalantly. **"After you were born there was a little piece missing from it, so I had to rest for a long time before I could do anything else. I started noticing after effects, mainly physical."**

 

"So that explains..." sans hovered a finger on his own left eye where his father had the crack.

 

 **"Yes, those ones in particular…"** He placed his soul back into his chest with a grunt. **"One day I had enough of waiting and decide to get to work. It took me a year to restore the machine as well as a few precautions to ensure this time it wouldn’t break. After some adjustments, it was done. I called Asgore just in case something went wrong, but I wasn’t going to wait for him, he would've tried to stopped me if he knew what I was about to do."**

 

**"This time the machine didn’t explode but the repercussion where the same. Because it was the second time I used a piece of my soul they were more intense."**

 

**"Asgore found me sitting in a chair holding Papyrus. He held him like he did with you, hehe, you should have seen that. Asgore would look up at me and scold me and then down to shush Papyrus and then back at me. I was so out of it I started to laugh. It only made him even angrier at me.**

 

 **"I was happy; the future looked brighter, I finally found the motivation to make an even greater effort on braking the barrier."** He looked at the ceiling, hands moving fast in sudden excitement.

 

 **"I want you two, to be able to breathe the fresh air, to feel the warmth of the sun, to see the sunrise and the night sky coated in stars. I want to have a future outside of this place with my family. Our family."** Gaster sat down next to sans. He turned to look at him with a stern look. **"So please, never think of yourself as an object or tool, because you aren't."** He grabbed sans hand squeezing it tightly.

 

 **"You are not WP01. You are Sans Aster. Brother of the Great Papyrus Aster, son of the Royal Scientist Dr. Wing Dings... Aster."** Sans eyes grew wide hearing his father say his complete name with a grimace, he couldn’t help a short giggle.

 

 **"You two are my sons. There is nothing in the world I love more than you two and knowing that you would hate me after that I..."** he looked at his hands, fidgeting with the ridge of his sweater. 

 

"no! dad I... I don’t...” he panicked all of a sudden. “I am angry and... feel a bit betrayed but... i don’t hate you." Sans instantly comforted his father "is just... is difficult to grasp, ya know? have to think about it for a while..." He scratched the back of his skull.

 

**"I... understand."**

 

"should we... should we tell papyrus?"

 

 **"I don’t know.... maybe when he's a bit older..."** he face forward not looking at anything in particular.

 

"Yeah... maybe..." he pocketed his hands on his hoodie realizing he still had his lab coat. “Heh... i think we are taking a bit too much time for a break."

 

 **"Eh... don’t mind right now."** He shrugged. **"Besides, we still haven’t had lunch..."** he said airy, tapping his fingers together. Sans looked at him a bit skeptical as Gaster stood up.

 

"you want to go back late? alright... now i really don’t know who you are." He said in a soft chuckle.  
Gaster looked back at him.

 

 **"Well... one cannot think clearly with an empty stomach."** He extended a hand to sans knowing full well he would be the one making the shortcut.

 

"gee boss... i don’t think i have the stomach to do another shortcut." Sans joked as he took his father's hand.

 

 **"Pfftt! I haven’t heart that one before."** He answered, his shoulders bouncing slightly from laughter.

 

"how lung do you think we'll take eating?"

 

**"Not too lung I hope."**

 

"hey! you can’t reuse puns" he scolded with a smile.

 

 **"I did not. There are two lungs. I just used the other one for mine."** Sans burst in laughter closely followed by Gaster's own trying to repress a snort. They teleported to the back of Grillby's in a fit of laugh. 

 

The bartender raised his head as the pair of giggling skeletons entered the bar, taking their respective seats at the bar.

 

'Well, aren’t you guys chipper.' He signed, there was too much people in there to be able to talk properly.

 

 **"Grillby, I kidney you not, today was quite a weird day."** Gaster said still laughing.

 

"liver and learn, that's what i always say." Followed sans finally getting his father to let out a snort.  
Grillby looked amused at both skeletons chuckling softly, their laughter becoming contagious.

 

**Author's Note:**

> I'm sorry if sans came out a little out of character, I mainly just wanted to put this up, I just wrote him how I thought he would react. I had the idea when thinking sans might have been an accidental discovery and then Gaster's dialog about 'Not being that special' and the last lines of dialog. Sorry if everything seems so forced, I not that good of a writer. 
> 
> Feedback is always appreciated. <3
> 
> I will work out a few other stories regarding Gaster's backstory as well as Post-Pacifist ones.  
> This story is tied with part of a series of comics I'm trying to do as well of other stories I have in mind that will be part of the same timeline that I'm just going to name for the moment "Truest Pacifist" because that's the first thing that crossed my mind. My tumblr is Noire73.tumblr.com where you can check the dad!Gaster comics I have there.


End file.
